Process control system



2 Sheets-Sheet 1 Oct. 3, 1961 D. E. BERGER PROCESS CONTROL SYSTEM FiledNo?. 28. 1956 A TTORNEVS Oct. 3, 1961 D. E. BERGER PROCESS CONTROLSYSTEM 2 Sheets-Sheet 2 Filed Nov. 28. 1956 RECYCLE ISOBUTANE-l AIR AIRSUPPLY OUTPUT CONTROLLER SERVO AMPLIFIER FTI I |6 I l LI r lp COMPUTERISOBUTANE ANALYZER OLEFI N PROPANE ISOBU TANE BUTANE PROPYLENE BUTYLEN EISOBUTANE ANALYZER ISOBUTANE (Cles-Fles) (Cno- FI75) (Cm-Fm) TTINVENTOR.

D. E. BERGER HMM* (M SERVO AMPLIFIER I Lf (C le 7- F les) lISO P175 T Lil lila A TTORNE V5 3,tll2,818 PRUCES CUNTRL SYSJI'EM Donald E. Berger,Bartlesville, Ghia., assigner to Phillips Petroleum Company, acorporation oi Delaware Filed Nov. 28, 11956, Ser. No. 624,843 i2claims. (ci. zsuass) This invention relates to an improved controlsystem for alkylation processes. ln another aspect, it relates to animproved control system for a fractionation column.

The demand for large volumes of high quality gasolines has brought aboutthe development and commercialization of a number of processes for theconversion of nongasoline range hydrocarbons into high octane blendingstocks. One of these processes, the alkylation of light olefins, such aspropylene and butylenes, with isobutane, using liquid hydrotiuoric acidas the catalyst, has proved to be particularly effective in producingalkylates for aviation and motor fuel blending. As the result ofconsiderable operational experience, this process has now been developedto such an extent that a commercial plant can be controlled by two menper shift to obtain desired product quality with safety. However, asubstantial expenditure of laboratory and process engineering time stillis required to coordinate the operations and to manipulate the processvariables toward the economic optimum.

ln accordance with the present invention, an improved control system forsuch an alkylation porcess is provided. The combined feed stream to thereactor, which comprises parati-ln and ole'lin hydrocarbons, is analyzedto determine the ratio of isoparaftlns to olens. A ratio controller isprovided to adjust the iiow of one or more of the feed streams inresponse to the analysis ratio so that the iso- 'parahins and olelinssupplied to the reactor can be maintained at a desired ratio to obtainoptimum economic operation. ln accordance with another aspect of thisinvention, an improved control system for a fractionation column isprovided. This control is based upon analyses of sample streams removedfrom both the upper and lower regions of the column. The heat andmaterial balances of the column are adjusted in response to theseanalyses so as to provide two output product streams of desiredcomposition. The alkylation process is also controlled in accordancewith this invention to limit the a-mount of non-reactive constituents,such as propane and normal butane in the system.

Accordingly, it is an object of this invention to provide an improvedcontrol system for an alkylation process.

Another object is to provide `a control system to adjust ratio ofisoparadins to olelins supplied to an alkyln ation reactor.

A further object is to provide a control system for a fractionationcolumn which operates to provide two product streams of desiredcompositions.

Dther objects, advantages, and features of this invention should becomeapparent from the following detailed de- United States Patent scriptionwhich is taken in conjunction with the accompanying drawing in which:

FIGURE l is a schematic representation of a hydroiluoric acid alkylationprocess having the control system of this invention incorporatedtherein.

FIGURE 2 is a schematic representation of an infrared analyzer which canbe employed in the control system of FlGURE l.

FGURE 3 is a schematic representation of a second embodiment of thecontrol system which regulates the ratio of isoparal'lins to olelinssupplied to the alkylation reactor.

FIGURE Ll is a schematic representation of a computer `which can beemployed in the control system of FIG- URE 3.

Referring to the drawing in detail and to FIGURE 1 icc in particular,there is shown an alkyla-tion reactor 10 which has an inlet conduit il.communicating therewith to supply liquid hydrouoric acid. A hydrocarbonfeed stream is introduced into reactor lli) through -a conduit l2. Anisobutane feed stream is supplied to inlet conduit l2 through a conduitlo. rllhe ilow through conduit 13 is regulated by a rate-of-ilowcontroller la which adjusts a valve l5. An olefin feed stream, which canbe a mixture of propylene and butylenes, for example, is supplied toconduit l2 through a conduit lo. The flow through conduit la isregulated by a rate-of-ow controller .l' which adjusts a valve 18. Thealkylation reaction is completed in reactor it) by intimately contactingthe hydrocarbons with the hydroiuoric acid catalyst. The hydroilucricacid-hydrocarbon mixture is removed from reactor through a conduit 2lwhich communicates with a settler 23. The acid phase in settler 23 iswithdrawn through a conduit 26 which communicates with an acidpuriiication unit 27. All, or a part, of this acid is puriiied in unit27 by distilling the acid from water and acid soluble oils. The ratio ofacid to hydrocarbons supplied to reactor it) is generally controlled ata selected level between approximately 0.211 to 1:1, parts by weight.

The hydrocarbon phase, which contains some soluble hydrotluoric acid, isremoved from settler 23 through a conduit 28 which communicates with theinlet of a fractionation column 33 that is operated as a deisobutanizer.Conduit 28 passes through a heat exchanger 29. A heating medium iscirculated through exchanger 29 by means of a conduit 3d. The tlow ofheating material through conduit 3d is regulated by a temperaturecontroller di which adjusts valve 32 in response to a measurement of thetemperature of the duid entering column 33. This insures that the feedstream is supplied to column 33 at substantially a constant temperature.

Column 33 is operated so as to separate the isobutane and lightercomponents from normal butano and the alkylate product. The normalbutane and allrylate product are withdrawn as a kettle product `fromcolumn 33 through a conduit The rate of withdrawal of kettle product isregulated by a liquid level controller 36 which adjusts a valve 37 so asto maintain a constant liquid level in column Column 33 is provided witha reboiler 7d. A. heating medium is circulated through reboiler 7o bymeans of a conduit 'il which is provided with a rate-of-tlow controller72 ti at adjusts a valve 73. The isobutane and lighter hydrocarboncomponents and soluble hydrotluoric acid are removed from the top ofcolumn 33 through a conduit itl which communicates with an accumulatorl2 through a condenser dl. The flow through conduit dil is controlled bymeans of a pre sure controller t3 which adjusts a valve 44. A by-passconduit is provided around condenser 4l. A pressure controller t7adjusts a valve do in conduit l5 to regulate the amount `of materialcondensed and cooled in order to maintain a predetermined pressure inaccumulator 4t2.

Hydroliuoric acid which settles out in accumulator 42 can be returned tothe reactor system through a conduit 48 which communicates with aconduit Sil, the latter communicating with conduit Zt. Conduit 4S isprovided with a valve d? so that the return of acid can be adjusted. Thecondensed hydrocarbons in accumulator 42 are withdrawn through a conduit52. A portion of these condensed hydrocarbons is returned to column 33as reflux through a conduit S3. The ilow through conduit 53 is regulatedby a rate-of-low controller 50i which adjusts a valve S5. The remainderof the condensed hydrocarbons Withdrawn from accumulator 42 is directedthrough a conduit 5d. A portion of this material is directed through aconduit 59 to a second fractionation column SS which is operated as adepropanizer. The iiow through conduit 59 3 is regulated by a rateofowcontroller 6d which adjusts a valve 61. A heater 57 is provided inconduit 59. Heat is supplied to heater 57 by means of a conduit 63 yandat a rate which is regulated by a temperature controller 62V 'whichadjusts a valve. 64. Temperature controller 62 responds to thetemperature of the duid passed through conduit 59 so that the feed tocolumn 58 is maintained at a constant temperature.

The major portion of the overhead product from column 33 is returned toreactor 16 through conduits 56, 75, and 12. The rate of liow throughconduit d6 is adjusted by a liquid level controllereti which regulates avalve 67 to maintain a constant liquid level in accumulator 42.

Column S8 is operated so as to separate propane and any hydrouoric acidwhich remains in the system from the unreacted isobutane. A kettleproduct stream., which comprises principally the unreacted isobutane, isremoved from column d through a conduit 75 which communicates withconduit i2. A cooler 76 is provided in conduit 75 to cool the isobutanethat is recycled to reactor 1d. The liow through conduit 75 is adjustedby a liquid level controller 77 which adjusts a valve 7d in conduit 75in response to the liquid level in column 58. Column 58 is providedVwith a reboiler 80. A heating medium is circulated through reboiler 80by a conduit 81 at a rate which is regulated by a temperature controller82 which adjusts a valve S3 in response to the temperature in the lowerregion of column 53. The overhead stream from column 53 is removedthrough a conduit 55 which commnnica'tes with an accumulator S7 througha condenser Se. A pressure controller 93 regulates a valve 94 in conduit85 so as' to maintain. a predetermined pressure in column 58. Coolant iscirculated through condenser 86 by means of a conduit titl. The flowthrough conduit 9i) is' regulated by a pressure `controller 91 thatadjusts a valve 92 to maintain a predetermined pressure in accumulator37. Any acid which may settle out in accumulator S7 can be returned tothe reactor system through conduit' 8S. A valve 3% is provided inconduit 33 to permit adjustment of the rate acid is returned to settler23. The condensed hydrocarbon liquid in accumulator d'7 is removedthrough a conduit lill. A portion of this condensed liquid is' returnedto column 53 as reflux through a conduit 9S. The tlow through conduit 9dis regulated by a rate-or-tlow controller 96 which adjusts a valve 97.The remainder of the liquid removed from accumulator 37 is directedthrough a conduit 93 to an acid stripper 95E. The rate of ilow throughconduit 9, is adjusted by a liquid level controller ltlil whichregulates a valve 106 in conduit 93 so as to maintain a constant liquidlevel in accumulstor 8'7.

Heat is supplied to the lower region of stripper @9 by means of areboiler lili. A heating medium is circulated through reboiler 114 bymeans of a conduit 11;?. A temperature controller 116, which isresponsive to the tema perature in the lower region of stripper 99,regulates a valve 117 in conduit 115. Any hydroiluoric acid which isintroduced into stripper 99 is vaporized and removed through a `conduit162 which communicates with accumulator 87. A predetgmined pressure ismaintained in stripper 99 by means of a pressure controller 193 whichadjusts a Valve 105 in conduit 162. Propane is withdrawn as the kettleproduct from stripper 99 through a conduit 11i) which has a cooler 111therein. rlie rate of withdrawal of propane through conduit llo isadjusted 'oy a liquid lever controller 112 which regulates a valve 113so as to maintain a constant liquid level in stripper 99.

Since the alkylation reaction is a chemical combination of one moleculeof isobutane with each molecule of olefin fed into the system, sulcientfresh isobutane must be added to match this consumption andfractionation losses. Also, for the purpose of operatingY the unit so asto produce a maximum amount of high quality product, a

considerable volume of isobutane is recycled Within the unit so that atthe reactor inlet' the Volume ratio of' isobutane -to total olens ismaintained at a predetermined ratio. This ratio is of the order of 4-6to l for the maximum economic production of motor fuel constituents,although this ratio Varies with different operations. The control systemlof the present invention is provided. to maintain this ratio at adesired value, To this end, a sample of the feed stream l2 to reactorlil is removed through a sample conduit'12t') which communicates with anoletin analyzer 12l and an isobutane analyzer 122. Analyzer 121 providesa first output signal which is representative of the concentration ofolefins supplied` to reactor 10. Analyzer 122 provides a second outputsignal which is representative of the concentration of isobutanesupplied to reactor 10. These two output signals are applied as therespective inputs to a ratio controller 123. Ratio controller 123provides an output signal which resets one of the liow controllers 14 or17. in this manner,4 the ratio of isobutane to oleiins supplied toreactor 1t) through conduit 12 is adjusted as necessary to maintain apredetermined ratio. This control can conveniently be made by regulatingthe isobutane iiow through conduit 13. Con.- troller 123 can be anyconventional commercially available instrument which provides an outputsignal that isa function of the ratio of the two input signals appliedthereto, such as, for example, the instrument described in Catalog 20-1(l945) of the Brown instrument Com,- pany, Philadelphia, Pa. Thiscontroller can conveniently operate by pneumatic pressure, for example.By means of this control system the ratio of isobutane to totalV oleinssupplied to reactor 1G is maintained at a desired value Jhich. resultsin the optimum economic production of motor fuel alkylates.

The operation of column' 33 is controlled in accordance with thisinvention in order to maintain the desired separation between normalbutane and isobutane. To this end, a first sample stream is removed fromthe upper region of column 33 through a conduit 12S which cornmunicateswith the inlet of a normal butane analyzer 126. A second sample streamis withdrawn from a lower region of column. 33 through a condut 127which communicates with an isobutane analyzer 128. Analyzer 126 providesan output signal which is employed to reset rate-of-ow controller S4 onreflux conduit 53. Analyzer 128 provides an output signal which isemployed to reset rate-offlow controller 72 which regulates the amountof heating medium supplied to reboiler 76. The concentration of normalbutane in the sample stream removed through conduit 125 normally isquite small because column 33 is operated to remove the normal butanethrough conduit 34. Analyzer 126 provides an output signal which isrepresentative of this concentration. lf normal butane concentrationshould exceed a predetermined value, for example, rate-of-llowcontroller 54 is reset so as to open valve v further to increase theredux rate. This serves to decrease the amount of normal butane in theupper region of column 33. Similarly, it is desired that the kettleproduct contain a minimum amount of isobutane. Analyzer 128 provides anoutput signal which is representative of the isobutane concentration ofthe lower region of column 33. If the measured isobutane concentrationshould increase above a preselected value, for example, analyzer 128resets rate-of-tlow controller 72 so as to open valve 73 further. Thisincreases the amount of heat supplied to reboiler so as to vaporize moreof the iluid in column 33, which results in a greater amount ofisobutane being removed as overhead product. It should thus be evidentthat the two analyzers 126 and 128 cooperate with one another in amanner so as to accomplish an elcient separation between the normalbutane and isobutane in column 33.

For satisfactory operation of the alkylation unit, propane must beremoved from the system at the same rate it may be ted into the systemby the inlet feed streams.

Vother non-absorbing gas or normal butane. -of cell 143 is to compensatefor the radiation absorbed A sample conduit 130 communicates betweenconduit 56 and the inlet of a propane analyzer 131. This analyzerprovides an output signal which is representative of the propaneconcentration in the stream directed through conduit 56. The outputsignal of analyzer 131 resets rateof-flow controller 69 so as toregulate the flow rate through conduit 59. If the measured propaneconcentration should increase, for example, rate-of-iiow controller 60is reset to open valve 61 further. This allows additional propane andisobutane to be directed to columns 58 and 99. The propane is eventuallyremoved from the system ai the kettle product from stripper 99. In thismanner, a build-up of propane in the alkylation unit is prevented.

The five analyzers employed in the control system of FIGURE 1 canadvantageously be infrared analyzers. A suitable analyzer of this typeis illustrated schematically in FIGURE 2. A iirst beam of radiation froman infrared source 141i is directed by means of a reflector 141 througha sample cell 145 and a filter cell 144 to impinge upon a firsttemperature sensitive electrical resistance element 145. A second beamof radiation from source 140 is directed by a reflector 146 throughsample cell 143 and a filter cell 148 to impinge upon a secondtemperature sensitive electrical resistance element 1511. Cells 143,144, and 148 are provided with windows 151 that are transparent to theinfrared radiation in the region of interest. These windows can beformed of quartz, for example. The sample stream to be' analyzed is introduced into cell 143 by means of an inlet conduit 152 and is removedthrough a vent conduit 153. A voltage source 155 is connected acrossresistance elements 145 and d which are connected in seriesrelationship. The

end terminals of a potentiometer 156 are connected to the respectiveterminals of voltage source 155. The junction between resistances 145and 15G', and the contactor of potentiometer 156 are connected to therespective input terminals of a servo amplifier 157. The output ofampliiier 157 is connected to a reversible servo motor 158. The driveshaft of motor 158 is connected to the contactor of potentiometer 156and to the input of a controller 160. Motor 155 can adjust a dappervalve in controller 160 to establish a pneumatic pressure representativeof the motor rotation.

It should be evident that the illustrated electrical cir- -cuitcomprises a modified form of alternating current URE 2 is to be employedto detect isobutane in sample streams 120 and 127, cell 144 can befilled with a pure sample of isobutane. Cell 14S can be filled with airor The purpose by the windows of lter cell 144 and absorption due toother components. The wave lengths of radiation which are absorbed byisobutane are removed from the radiation beam which is directed throughlter cell 144. The amount of radiation transmitted through cell 148 andvwhich impinges upon element 150 is a function of the isobutaneconcentration in sample cell 143. Any change in this concentrationchanges the ratio of the amounts of radiation impinging upon elements145 and 150. Such a change in the electrical resistances of theseelements changes the electrical unbalance of the bridge network. Theamount of rotation of motor 158 which is needed to restore a balancer-1condition in the bridge is thus representative of the change inisobutane concentration in sample cell 143. The rotation of motor 15S isapplied to controller 160. If controller 160 is a pneumatic instrument,for example, the drive shaft of motor 158 can be connected throughsuitable mechanical linkages to regulate a flapper valve in controller160 to adjust the output air pressure. A telemetering potentiometer cand be employed if it is desired to utilize an electrical`con= troller. Inany event, controller provides an output signal which is representativeof the concentration of isobutane in the sample cell.

When the analyzer in FIGURE 2 is employed as ana# lyzer 126 of FIGURE l,normal butane is positioned in filter cell 144. Similarly, an olefin ora mixture of oleiins to be detected is positioned in filter cell 144when the analyzer is employed as instrument 121 of FIGURE 1 to measurethe concentration of oleins. Sample cell 144 can be filled with propanewhen the instrument of FIGURE 2 is employed at analyzer 131 of FIGURE 1.

In FIGURE 3 there is shown a second embodiment of the control system ofthis invention which is particularly useful if it is desired that thefeed streams not be comf bined prior to their introduction into thealkylation reactor. In the system of FIGURE 3, the recycle isobutaneconduit 654-75 Iand the fresh isobutane conduit 13" are connected to acommon inlet conduit 163 of reactor 1li. The olens are introduced intoreactor 1G through a conduit 1d. Sample conduits 164 and 166 communicatebetween inlet conduit 16 and the inlets of an isobutane analyzer 165 andan olefin analyzer 167, respectively. A third sample conduit 169communicates between conduit 1.63 and thepinlet of an isobutane analyzer170i. Isobutane analyzer 165 is provided because there are moderateamounts of isobutane in the olefin feed stream. The output signals ofanalyzers 165, 167, and 170, which represent the concentrations ofisobutane, oleiins, and isobutane, respectively, are applied to theinputs of a computer network 173. A flow transmitter 158 provides afourth input signal to computer 173 which is representative of the flowrate through conduit 16'.' A econd iiow transmitter 175 provides a fifthinput signal to computer 173 which is representative of the iiow lratethrough conduit 163. The computer 173, which can be an analogue or adigital computer, provides an output signal which is representative ofthe ratio by volume of the isobutane to total olens supplied to reactor1t). This computer effectively solves the following equation andprovides an output signal representative thereof:

Volume of isobutane: (CX65-F158) -l- (Cntr F115) Volume of olens(Gis1-Fmt) where C155 is the isobutane concentration measured byanalyzer 165, C170 is the isobutane concentration measured by analyzer170, C167 is the oleiins concentration measured by analyzer 167, F158 isthe rate of flow through conduit 16', and F175 is the rate of flowthrough conduit 165. In this manner, the desired volumetric ratiobetween isobutane and olefins to reactor 1t) is maintained by controller14' being reset by the output signal of computer 173.

A computer 173 which can be employed in the control system of FIGURE Sisillustrated schematically in FIG- URE 4. Flow indicators 168 and 175 ofFIGURE 3 provide electrical output signals representative of therespective measured flows. These input voltages F168 and F175 areapplied to the illustrated input terminals. of FIGURE 4. The upperterminal F158 is connected to ground through a potentiometer 151i. Thecontactor of potentiometer 1S@ is connected through a high valueisolating resistor 181 to the input of a summing ampliier 182. TerminalF175 is connected to ground through a potentiometer 153. he contactor ofpotentiometer 183 is connected through a high value isolating resistor184 to the input of summing amplifier 182. The contactors ofpotentiometers 181i and 183 are adjusted by motors 158g and 15317,respectively, which represent the motors 153 of analyzers 165 and 170,respectively. The motors are connected to the contactors of thepotentiometers so as to move upwardly if the analyzer outputs increaseand downwardly if the analyzer outputs decrease, thereby to perform theindicated multiplications. The output of amplifier 182 is connected toground through a potentiometer 186. The second terminal Flea is connected to ground through a potentiometer 187. The contactor ofpotentiometer 187 is connected to the input of a servo amplifier 188which energizes a reversible servo motor 189. Amplifier 18S can be aconventional instrument which compares the input voltage with areference voltage, converts the difference to a corresponding A.C.signal, and provides an output signal of phase represent-ative of theinput signal being greater or less than a reference value. Such anamplifier is described in detail in Electronic Control Handbook, Batcherand Moulic, 1946, page 298. The contactor of potentiometer 187 isadjusted by a motor 158e which represents the output of analyzer 167.Motor 189 is set to move the contactor of potentiometer 186 in adirection to divide the voltage across the potentiometer by the inputvoltage to amplifier 188. Thus, if the input voltage to amplifier 188increases, the contactor of potentiometer 186 is moved downwardly todecrease the quotient voltage at the contacter of potentiometer 186. Themagnitudes ofthe vari ous voltages are calibrated to provide theindicated output signal. This signal, resets controller 14.

As a specific example of this invention, reactor 1t? is operated at 901F. and at a sufficient pressure to maintain a liquid state. The ratio ofis'obutane to olefins supplied to, reactor 10, based on parts by weight,is six to one. Hydouoric acid of 92 weight per cent purity is employedas the catalyst. This acid is supplied to reactor at a ratio of one-halfto one, based on catalyst to hydrocarbon parts by weight. Column 33 isoperated at 160 p.s.i.g., 165 F. top temperature, 280 F. bottomtemperature, and a reux to feed ratio of two to. one. Column 58 isoperated at 285 p.s.i.g., there being a pump, not shown, between columns33 and 58, 140 F. top temperature, and 220 F. bottom temperature. Thecompositions and flow rates through the several conduits are as follows:

Conduit 16 13' 2s at 5s 110 sts-Me Propy1ene.. 2, 021 v.... ...n Propane9 54 l, 559 l, 569 1,025 544 Butylenes 2, Isobutane 1, 49h 3, 028 17,536 120 17, 416 20 17, 396 NormalA B tane 2, 341 106 4, 007 2, 447 1,550 1, 560 .Alkylate..- ....Y 7,460 ,460

The above gures are in barrels per day, based on condensed liquids Fromthe foregoing it should be evidentv that there is provided in accordancewith this invention an improved control system for an allrylation unit.By controlling the ratio of reactants fed to the alkylation reactor, itis possible to operate the unit in an automatic manner so as to providea maximum amount of desired product. While the invention has beendescribed in conjunction withl a particular reaction of isohutane withlight olefins, it should be evident that it is not limited to thisspecific reaction. Also, the fractionation column control system isadaptable to any system wherein is is desired to separate a 'uid mixtureinto two or more product streams of desired composition.

While the invention has been described in conjunction with a presentpreferred embodiment, it should be evident that it is not limitedthereto.

What is claimed is:

l. In an `allrylation unit wherein a mixture of olefins and isoparafinsis contacted by a catalyst in a reactor; a control system to maintain apredetermined ratio of olens to isoparaffins in the hydrocarbon feed tothe reactor comprising first conduit means communicating with saidreactor to supply olefins, second conduit means `communicating with saidreactor to supply isoparains, first `analyzing means to measure the flowof olefins by detecting the concentration of olefins supplied throughsaid rst conduit mea-ns, second analyzing means to measure; the. fiow ofisoparaliins by detecting the concentration of isoparafiins suppliedthrough said second conduit means, and means responsive *o said firstand second analyzing means toy adjust the fiow through at least one ofsaid conduit means to maintain a predetermined ratio of olefins toisoparains in the hydrocarbon feed to the reactor.

2. In an alkylationl unit wherein a mixture of olefins and isoparafiinsis contacted by a catalyst in a reactor; a control system to maintain apredetermined ratio of olefins to isoparafiins in the hydrocarbon feedto the reactor comprising a first conduit communicating with saidreactor to introduce the hydrocarbon feed mixture, first conduit meanscommunicating with said first conduit to supply oletins, second conduitmeans communicating with said first conduit to supply isoparafiins, rstanalyzing means to measure the ow of olefins by detecting theconcentration of oleins supplied through said iirst conduit, secondanalyzing means to measure the ow of isoparafiins by detecting theconcentration of isoparaliins supplied through said rst conduit, andmeans responsive to said tirst and second analyzing means to adjust thefiow through at least one of said conduit means to maintain apredetermined ratio of oleiins to isoparains in the hydrocarbon feed tothe reactor.

3. ln an alkylation unit wherein a mixture of olefins and isoparafiinsis contacted by a catalyst in a reactor, and wherein at least a portionof the unreacted isoparaiiins is separated from the reactor efiluent andrecycled to the. reactor;` a control. system to maintain apredetermined. ratio of oleiins to isoparafiins in the hydrocarbon feedto the reactor comprising an inlet conduit com municating with saidreactor, first conduit means com.- municating with said inlet conduit tosupply olefins, second conduitr means communicating with said inletconduit to. supply fresh isoparatlins, third conduit means communicatingwith said inlet conduit to supply recycled isoparaflins, first analyzingmeans to measure the tiow of oleiins by detecting the concentration ofolens supplied through said inlet conduit, second analyzing means tomeasure the flow of isoparahns by detecting the concentration ofisoparafiins supplied through said inlet conduit, and means responsivetol said first and second analyzing means to adjust the flow through atleast one of said conduit means to maintain a predetermined ratio ofolefins to isoparafins in the hydrocarbon feed to the reactor.

4. In an allcylation unit wherein a mixture of olefins and isoparafiinsis contacted by a catalyst in a reactor, and wherein at least a portionof the unreacted isoparafrins is separated from the reactor eiiiuent andrecycled to the reactor; a control system to maintain a predeterminedratio of olefinsr to isoparafiins in the hydrocarbon eed to the reactorcomprising first conduit means communicating'. with said reactor tosupply olens, second conduit means communicating with said reactor,third conduit means. communicating with said second conduit means tolsupply fresh isoparafiins, fourth conduit means communicating with saidsecond conduit means to supply recycled isoparatiins, first analyzingmeans to measure the flow of olefins by detecting the concentration ofolefins supplied through said first conduit means, second analyzingmeans to measure the flow of isoparaflins by detecting the concentrationof isoparatlins supplied through said second conduit means, and meansresponsive to said first and second analyzing means to adjust the fiowthrough at least one of said conduit means to maintain a predeterminedratio of olefins to isoparains in the hydrocarbon feed to the reactor.

5. In an alkylation unit wherein a mixture of olefins and isoparafiinsis contacted by a catalyst in a reactor, and wherein at least a portionof the unreacted isoparains is separated from the reactor eiiiuent andrecycled to the reactor; a control system to maintain a predeterminedratio of oleiins to isoparafiins in the hydrocarbon feed to apuesta thereactor comprising tirst'conduit means communicating with said reactorto supply olefins, second conduit means communicating-with said reactor,third conduit means communicating with said second conduit means tosupply fresh isoparafiins, fourth conduit means communicating with saidsecond conduit means to supply recycled isoparafiins, rst analyzingmeans to measure the concentration of olefius in said iirst conduitmeans, second analyzing means to measure the concentration of isoparainsin said second conduit means, first fiow measuring means to measure theilow through said rst conduit means, second flow measuring means tomeasure the flow through said second conduit means, and means responsiveto saidvrst and second analyzing means and said first and second owmeasuring means to adjust the iiow through at least one of said conduitmeans to maintain a predetermined ratio of olefins to isoparafiins inthe hydrocarbon feed to the reactor.

6. Apparatus for separating a fluid mixture of at least two componentshaving different boiling points into tirst and second streams comprisinga fractionation column, means to introduce the fluid mixture to beseparated into said column, means to supply heat to said column, meansto withdraw a kettle product stream from said column, an accumulator, acondenser, means to pass vapors from the upper region of said columnthrough said condenser to said accumulator, means to pass iiuid Afromsaid accumulator to said column as reflux, means to withdraw a rstsample stream from the upper region of said co1- umn, rst means toanalyze said tirst stream to measure the concentration of the higherboiling component of the mixture being separated, means responsive tosaid rst means to analyze to adjust the reiiux fiow to maintain themeasured concentration of said higher boiling component less than apredetermined value, means to withdraw a seco-nd sample stream from thelower region of said column, second means to analyze said second streamto measure the concentration of the lower boiling component of themixture being separated, and means responsive to said second means toanalyze to adjust the heat supplied to said column to maintain themeasured concentration of the lower boiling component less than apredetermined value.

7. Apparatus for separating a iiuid mixture of at least two componentshaving diierent boiling points into first and second streams comprisinga fractionation column, means to introduce the iiuid mixture to beseparated into said column, means to supply heat to said column, meansto withdraw a kettle product stream from said column, an accumulator, acondenser, means to pass vapors from the upper region of said columnthrough said condenser to said accumulator, means to pass fluid fromsaid accumulator to said column as reiiux, means to remove iiuid fromsaid accumulator as a second product, means responsive to the liquidlevel in said accumulator to regulate the rate of removal of said secondproduct to maintain a predetermined liquid level in said accumulator,means responsive to the liquid level in said column to regulate the rateof withdrawal of said kettle product to maintain a predetermined liquidlevel in said column, means to withdraw a first sample stream from theupper region oi' said column, first means to analyze said rst stream tomeasure the concentration of the higher boiling component of the mixturebeing separated, means responsive to said iirst means to analyze toadjust the reiiux slow to maintain the measured concentration of saidhigher boiling component less than a predetermined value, means towithdraw a second sample stream from the lower region of said column,second means to analyze said second stream to measure the concentrationof the lower boiling component of the mixture being separated, and meansresponsive to said second means to analyze to adjust the heat suppliedto said column to maintain the measured concentration of the lowerboiling cornponent less than a predetermined value.

8. An alkylation unit comprising a reactor; means to supply olefins andisoparafiins to said reactor; a iirst fractionation column adapted toseparate normal butane and higher boiling constitutents from isobutaneand lower boiling constituents; means to pass the reaction products fromsaid reactor to said first fractionation column; a second fractionationcolumn adapted to separate propane and lower boiling constituents fromisobutane and higher boiling constituents; means to direct a first partof the overhead product from said first column to said second lcolumn asa rst stream; means to direct a second part of the overhead product fromsaid first column to said reactor as a second stream; means to measurethe propane concentrations of the overhead product of said first column;and means responsive to said means to measure to control the ratio ofsaid rst and second streams to maintain the measured propaneconcentration less than a predetermined value.

9. An alkylation unit comprising a reactor; means to supply oleins andisoparaiiins to said reactor; a first fractionation column adapted toseparate normal butane and higher boiling constituents from isobutaneand lower boiling constituents; means to pass the reaction products fromsaid reactor to said first fractionation column; means to remove a iirstpart of the overhead product from said iirst column as a first stream;means to direct a second part of the overhead product from said iirstcolumn to said reactor as a second stream; means to measure the propaneconcentration of the overhead product of said irst column; and meansresponsive to said means to measure to control the ratio of said firstand second streams to maintain the measured propane con'- centrationless than a predetermined value.

l0. An alkylation unit comprising a reactor; means to supply olefins andisoparafiins to said reactor; a first fractionation column adapted toseparate normal butane and higher boiling constituents from isobutaneand lower boiling constituents; means to pass the reaction products fromsaid reactor to said first fractionation column; a condenser; a refiuxaccumulator; means to remove iiuid from the top of said first column andpass same through said condenser to said accumulator; means to return aportion of the liquid in said accumulator to said first column as reux;means to remove a second part of the liquid from said accumulator as afirst stream; means todirect a third part of liquid from saidaccumulator to sa1d reactor at a rate to maintain a predetermined liquidlevel in said accumulator; means to measure the propane concentration inthe liquid removed from said accumulator; and means responsive to saidmeans to measure to control the fiow of said iirst stream to maintainthe maelasured propane concentration less than a predetermined v ue.

11. lA11 alkylation unit comprising a reactor, an inlet conduitcommunicating with said reactor, rst conduit means communicating withsaid inlet conduit to supply olefins, second conduit means communicatingwith said inlet conduit to supply isoparaiiins, a fractionation column,means to pass the reaction products from said reactor to saidfractionation column, means to supply heat to said column, means toWithdraw a kettle product stream from said column, an accumulator, acondenser, means to pass vapors from the upper region of said columnthrough said condenser to said accumulator, means to pass Huid from saidaccumulator to said column as reflux, means to withdraw a iirst samplestream from the upper region of said column, first means to analyze saidfirst stream to measure the concentration of the higher boilingcomponent of the mixture being separated, means responsive to said iirstmeans to analyze to adjust the reflux fiow to maintain the measuredconcentration of said higher boiling component less than a predeterminedvalue, means to withdraw a second sample stream from the lower region ofsaid column, second means to analyze said, second stream to measure theconcentration of the lower boiling component of. the mixture beingseparated, means responsive to said second means to analyze to ad` justthe heat supplied to said column to maintain the measured concentrationof the lower boiling' component less than a predetermined value, meansto Withdraw a first product stream from said accumulator', means to passlluid from said accumulator to said reactor, means to measure thepropane concentration in the uid Withdrawn from said accumulator, andmeans responsive to said means to measure to control one of the fluidstreams withdrawn from said accumulator to fmaintainthe measured propaneconcentration less than a predetermined value. l

12. An alltylation unit comprising a' reactor, an inlet conduitcommunicating with sa'id` reactor, rst conduit means communicating withsaid inlet conduit to supply olens, second conduit means communicatingwith said inlet conduit to supply soparainm a fractionation co1- umn,means to pass the reaction products froms'aid reactor to saidfractionation column, means to supply heat to said column, means towithdraw a kettle product stream from said column, an accumulator, acondensen, means to pass vapors from the upper region of said columnthrough said condenser to said accumulator, means to pass iiuid fromsaid accumulator to said. column as. reflux, means to withdraw a rstsample stream from the, upper region of said column,l first means toanalyze said first stream to measure the concentration of the, higherboiling component of the mixture being sepanated, meansr responsive tosaid rst means to analyze to adjust the reflux new to maintain themeasured' concentration of said higher boiling component less than apredetermined Value, means to Withdraw a' second sample stream from thelower region of said column, second means to analyze said second streamto measure the concentration of the lower boiling component of themixturev being separated, means responsive to said second means toanalyze to adjust the heat supplied to said columnv to maintain themeasured concentration of the lower boiling component less than apredetermined value, means to Withdraw a first product stream from saidaccumulator, means to pass fluid from said accumulator to said reactor,means to measure the propane concentration in the uid 'withdravtni fromsaid accumulator, means responsivev to said means to measure to controlone of the fluid streams withdrawn from said accumulator to maintain the-rneas'- ured propane concentration less than a predetermined value,third analyzing means to measurel the flow of olens by detecting theconcentration of olens supplie' through said inlet conduit, fourthanalyzingmeans to' measure the flow of isoparains by detecting theconcentration of isoparains supplied through said inlet conduit, andmeans responsive to said third and fourth analyzing means to adjust theiow through at least one of said conduit means to maintain apredetermined ratio of olens to isoparans in the hydrocarbon feed to thereactor.

References Cttee in the are of this patent UNITED STATES" PATENTS;

2,518,307 Groebe Aug';l 8,- L95() 2,574,006 Allen e Nov.v 6, 19512,602,046 Podbielniak July i, 11952 2,666,691 Robinson'. Ian. 19, 195421,696,464 Mathis Dec. 7, 1954 2,726,936 Bornheim Dec. 13,- i9552,759,032 Dixon Y Aug. 14, 1956 2,780,456 Berwaerts A Feb. 5, 195,72,868,216 Robertson Ian: 1-3, 1959 2,872,493 Hann Feb. s, 1959 2,881,235Vanv Pool Apr. 7,4 1959 OTHER REFERENCES- Brattain: Cal- Oil World` andPetroleum lud, pages 9 17, January/'1943. A

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1. IN AN ALKYLATION UNIT WHEREIN A MIXTURE OF OLEFINS AND ISOPARAFFINS IS CONTACTED BY A CATALYST IN A REACTOR, A CONTROL SYSTEM TO MAINTAIN A PREDETERMIEND RATIO OF OLEFIN TO ISOPARAFFINS IN THE HYDROCARBONS FEED TO THE REACTOR COMPRISING FIRST CONDUIT MEANS COMMUNICATING WITH SAID REACTOR TO SUPPLY OLEFINS, SECOND CONDUIT MEANS COMMUNICATING WITH SAID REACTOR TO SUPPLY ISOPARFFINS, FIRST ANALYZING MEANS TO MEASURE THE FLOW OF OLEFINS BY DETECTING THE CONCENTRATION OF OLEFINS SUPPLIED THROUGH SAID FIRST CONDUIT MEANS, SECOND ANALYZING MEANS TO MEASURE THE FLOW OF ISOPARAFFINS BY DETECTING THE CONCENTRATION OF ISOPARAFFINS SUPPLIED THROUGH SAID SECOND CONDUIT MEANS, AND MEANS RESPONSIVE TO SAID FIRST AND SECOND ANALYZING MEANS TO ADJUST THE FLOW THROUGH AT LEAST ONE OF SAID CONDUIT MEANS TO MAINTAIN A PREDETERMINED RATIO OF OLEFINS TO ISOPARAFFINS IN THE HYDROCARBON FEED TO THE REACTOR. 